The field of this invention relates to automatic welding apparatuses and more particularly to a welding assembly, which is designed primarily to facilitate welding of a pair of tubes, one of which protrudes from a tube sheet.
A heat exchanger typically consists of a shell in which are located a large number of parallel tubes through which a liquid is conducted. Steam is caused to flow into the shell, heating the tube, and therefore, heating the liquid that is in the tube. At both ends of the heat exchanger the tubes are held in their fixed position by the tube sheet. These spaced apart tubes sheets separate the steam containing shell interior from the remaining portion of the heat exchanger.
In a typical heat exchanger, there may be literally hundreds (in number) of tubes mounted in a closely spaced arrangement within the tube sheet. One tube from the tube sheet is normally connectd through a U-shaped connecting conduit to a directly adjacent tube. This connecting procedure is repeated for the mass of tubes extending from the tube sheet. It is necessary to insure that each joint connecting the connecting conduit to each tube is leakless. It has been found in the past that the best procedure to insure a leakless joint is by welding.
It has been found that manual welding of each of the tubes produces an insufficient quality weld. The inherently repetitive creating of each annular weld results in an occasional poor quality weld. Even if a single tube is found to leak, that leak must be repaired. Therefore, some means must be utilized to achieve a 100% weld quality at every weld.
In order to achieve this 100% weld quality, it is common to use an automatic welding apparatus. The automatic welding apparatus is securable in a set position with respect to the welding area. Desirable weld quality is obtained through the use of an inert gas environment to the tio of the welding electrode. The welding electrode and voltage is monitored by the use of a computer and instantaneous changes will be made if preset desirable parameters are not met during the welding procedure.
It is desirable for some means to be utilized to facilitate mounting of the welding head assembly in exactly the correct position with each pair of tubes that is to be welded. Upon welding of a particular pair of tubes, it is desirable to move as quickly and as easily as possible the welding head to a different pair of tubes and precisely locate such so that the weld with the next pair of tubes can now be accomplished. The structure of the present invention is designed in particular to produce repetitive welding of tubes which are precisely located in respect to a tube sheet.